[PATCH 07/10] of: add watchdog bootarg directly instead of via a globalvar

[Sascha Hauer <s.hauer@pengutronix.de>]

With CONFIG_SYSTEMD_OF_WATCHDOG, the device tree bootargs fixup puts
systemd.watchdog_device= into global.linux.bootargs.dyn.watchdog only to
read it back right away via linux_bootargs_get(). This has side effects
beyond the fixup:

 - The variable is created whenever the fixup runs, so also for of_dump
   -F, oftree -s or of_diff after a boot attempt has enabled the
   watchdog, and stays around afterwards.
 - Its mere existence makes linux_bootargs_get() ignore the legacy
   bootargs environment variable, which is only used when no
   global.linux.bootargs.* variables exist.

Return the option from watchdog_build_bootargs() and append it to the
bootargs in of_write_bootargs() instead. Note this moves the option to
the end of the command line, while it was previously sorted among the
global.linux.bootargs.* variables.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 Documentation/user/booting-linux.rst |  2 ++
 common/Kconfig                       |  6 +++---
 common/oftree.c                      | 41 ++++++++++++++++++++----------------
 3 files changed, 28 insertions(+), 21 deletions(-)

diff --git a/Documentation/user/booting-linux.rst b/Documentation/user/booting-linux.rst
index 0fbdc52c68..158aa8b313 100644
--- a/Documentation/user/booting-linux.rst
+++ b/Documentation/user/booting-linux.rst
@@ -124,6 +124,8 @@ interleaved with externally provided command-line arguments:
   * ``systemd.machine_id=`` controlled by :ref:`global.bootm.provide_machine_id <magicvar_global_bootm_provide_machine_id>`
   * ``systemd.hostname=`` controlled by :ref:`global.bootm.provide_hostname <magicvar_global_bootm_provide_hostname>`
   * ``barebox.security.policy=`` controlled by :ref:`global.bootm.provide_policy <magicvar_global_bootm_provide_policy>`
+  * ``systemd.watchdog_device=`` controlled by ``CONFIG_SYSTEMD_OF_WATCHDOG``,
+    only when booting with a device tree
 
 Creating root= options for the Kernel
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/common/Kconfig b/common/Kconfig
index 9adecfd2e4..da4cc8a5c9 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -1443,9 +1443,9 @@ config SYSTEMD_OF_WATCHDOG
 	bool "inform devicetree-enabled kernel of used watchdog"
 	depends on WATCHDOG && OFTREE && FLEXIBLE_BOOTARGS
 	help
-	  Sets the linux.bootargs.dyn.watchdog global variable with a value of
-	  systemd.watchdog_device=/dev/WDOG if barebox succeeded in enabling
-	  the watchdog WDOG prior to boot. WDOG is the alias of the watchdog
+	  Appends systemd.watchdog_device=/dev/WDOG to the Kernel command line
+	  in the device tree if barebox succeeded in enabling the watchdog
+	  WDOG prior to boot. WDOG is the alias of the watchdog
 	  in the kernel device tree. If the kernel is booted without a device
 	  tree or with one that lacks aliases, nothing is added.
 
diff --git a/common/oftree.c b/common/oftree.c
index 7aaed70e40..5f9b2e50cb 100644
--- a/common/oftree.c
+++ b/common/oftree.c
@@ -160,22 +160,18 @@ static int of_fixup_bootargs_reset_source(struct device_node *root,
 	return of_property_write_string(chosen, "reset-source-device", np->full_name);
 }
 
-static void watchdog_build_bootargs(struct watchdog *watchdog, struct device_node *root)
+static char *watchdog_build_bootargs(struct watchdog *watchdog, struct device_node *root)
 {
 	int alias_id;
-	char *buf;
 
 	if (!watchdog)
-		return;
+		return NULL;
 
 	alias_id = watchdog_get_alias_id_from(watchdog, root);
 	if (alias_id < 0)
-		return;
-
-	buf = xasprintf("systemd.watchdog_device=/dev/watchdog%d", alias_id);
+		return NULL;
 
-	globalvar_add_simple("linux.bootargs.dyn.watchdog", buf);
-	free(buf);
+	return xasprintf("systemd.watchdog_device=/dev/watchdog%d", alias_id);
 }
 
 static int bootargs_append = 0;
@@ -183,31 +179,40 @@ BAREBOX_MAGICVAR(global.linux.bootargs_append, "append to original oftree bootar
 
 static int of_write_bootargs(struct device_node *node)
 {
-	const char *str;
+	const char *str, *oldstr;
+	char *watchdog = NULL;
 	char *buf = NULL;
 	int ret;
 
 	if (IS_ENABLED(CONFIG_SYSTEMD_OF_WATCHDOG))
-		watchdog_build_bootargs(boot_get_enabled_watchdog(), of_get_parent(node));
+		watchdog = watchdog_build_bootargs(boot_get_enabled_watchdog(),
+						   of_get_parent(node));
 
-	str = linux_bootargs_get();
-	if (!str)
-		return 0;
+	str = skip_spaces(linux_bootargs_get() ?: "");
+
+	if (watchdog) {
+		if (*str)
+			str = buf = xasprintf("%s %s", str, watchdog);
+		else
+			str = watchdog;
+	}
 
-	str = skip_spaces(str);
 	if (strlen(str) == 0)
 		return 0;
 
 	if (bootargs_append) {
-		const char *oldstr;
-
 		ret = of_property_read_string(node, "bootargs", &oldstr);
-		if (!ret)
-			str = buf = xasprintf("%s %s", oldstr, str);
+		if (!ret) {
+			char *tmp = xasprintf("%s %s", oldstr, str);
+
+			free(buf);
+			str = buf = tmp;
+		}
 	}
 
 	ret = of_property_write_string(node, "bootargs", str);
 	free(buf);
+	free(watchdog);
 	return ret;
 }
 

-- 
2.47.3